This invention relates to slide fasteners and particularly to stringer tapes of a warp-knitted structure for mounting thereon rows of interlocking fastener elements.
There are known various types of warp-knitted tapes for use in the field of slide fasteners or zippers. Warp-knitted tapes of the known type are basically constructed with longitudinally extending chain stitches which form a multiplicity of wales and transversely extending lapping threads laid in to connect the wales coursewise. However, due primarily to their structural characteristics, the knitted tapes are known to be inferior to woven fabric tapes in respect of the qualities of mechanical strength and dimensional stability; that is, they have the inherent problem of "stretch" which occurs warpwise or weftwise when they are subjected to external stresses exerted in normal use of the slide fastener.
Many attempts have been made to eliminate the above problem and have proven successful to some extent in providing knitted fastener tapes which are rendered resistant to such stretch and which have a longitudinal marginal edge portion thickened or otherwise reinforced with use of a filling core so as to stabilize the position of fastener elements mounted thereon. However, the knit structure of the marginal edge portion of the prior-art tape was not sufficiently tight to retain the fastener elements in position over extended periods of use, the result being that the fastener elements become displaced or detached from their support tape under the influence of severe stresses applied in normal use of the slide fastener. This tendency is pronounced with the type of fastener elements which is designed to be mounted astride of the marginal edge of the knitted tape because such edge is not configured to conform with the shape of the legs of each element. Due to the coarse-structure of the marginal edge portion of the knitted tape, the filling core inserted therealong was also prone to shift out of place longitudinally of the tape.